The invention relates to strip tensioning apparatus and more particularly to apparatus for maintaining moving vertically-oriented strips at an established tension to prevent deformation thereof.
Even more particularly, the invention relates to such apparatus wherein the strip is metallic and relatively thin and flexible, such as metallic strip used in the production of aperture masks for color television cathode ray tubes.
The manufacture of aperture masks of the nature described usually involves a continuous process wherein a relatively long strip of metallic material is passed through a plurality of processing operations whereby the material is cleaned, coated with a photoresist material, exposed to a desired pattern, developed, etched, and the individual masks removed therefrom. A typical thickness for aperture mask metal is approximately 0.006 inch, with many of the individual masks on a typical strip having a diagonal dimension exceeding 23 inches. As can be appreciated, this material in strip form is relatively flexible thus making it imperative during the above-described processes that the strip not be permitted to flex or similarly deform. Accordingly, it is essential that the strip be continuously maintained at a desired degree of tension in order to prohibit such deformation.
Prior art devices which maintained a satisfactory degree of tension on a moving vertically-oriented metallic strip have required positioning of the device's motion apparatus above the strip. It was considered necessary to position these components in said manner to accomplish the tension. In the production of color television aperture masks, a typical pulling force of 1,000 pounds is exerted on a strip typically 26 inches wide and 0.006 inch thick, thus requiring a relatively heavy-duty tensioning apparatus.
A preferred location for tensioning apparatus for use in processing aperture mask strip is between the photoresist coating operation and the exposure station on the mask line. On many occasions, contaminants such as oil, grease, etc. spilled from the device's drive and gear mechanisms located above the coated strip. As a result, said contaminants formed on the phtosensitive material coating and were subsequently passed into the exposure station. These contaminants adversely affected the exposure operation with the result being the necessary rejection of several masks.
It is believed therefore that an apparatus which maintains a vertically oriented moving strip of relatively thin and flexible metallic material at an established tension in addition to preventing deformation and contamination thereof would constitute an advancement in the art.